JP2019119623A - Silicon carbide single crystal ingot and method for manufacturing silicon carbide single crystal - Google Patents

Abstract

To provide a silicon carbide single crystal ingot capable of reducing the number of TSD in a range capable of maintaining high quality.SOLUTION: A silicon carbide single crystal ingot 101 formed on a main surface having an offset angle to a c plane in the surfaces of a silicon carbide seed crystal 102 has a necking portion 101c depressed on the central-axis Cside of the silicon carbide single crystal ingot 101 in an outer-peripheral portion including at least a part on the offset downstream side except at least a part on the offset upstream side at a predetermined position P in the crystal growth direction D of the silicon carbide single crystal ingot 101.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a silicon carbide single crystal ingot and a method of manufacturing a silicon carbide single crystal.

  Silicon carbide (SiC), which is a semiconductor material, has a large band gap compared to Si (silicon) widely used as a substrate for devices. Therefore, power devices using a silicon carbide single crystal substrate, high frequency devices, high temperature operation Research has been conducted to produce devices and the like.

  These devices are formed on a silicon carbide single crystal substrate obtained by cutting out from a silicon carbide single crystal ingot grown by a sublimation method or the like, by the chemical vapor deposition (CVD) method or the like. It forms using the SiC epitaxial wafer which formed the epitaxial layer (film | membrane) which becomes.

  The silicon carbide single crystal substrate internally includes crystal defects called threading screw dislocation (TSD), and the device characteristics may be degraded by propagating to a SiC epitaxial film immediately above. In order to prevent device degradation caused by TSD, various techniques for reducing the number of TSDs inherent in a silicon carbide single crystal substrate have been studied.

  For example, in Patent Document 1, in the initial stage of silicon carbide single crystal growth, the outer peripheral portion of the silicon carbide single crystal is formed by narrowing the diameter so as to be smaller than the silicon carbide seed crystal (necking). A technique for sweeping out existing TSDs has been proposed.

JP, 2007-176718, A

  However, when necking is performed according to the method disclosed in Patent Document 1, the TSD is swept out over the entire outer peripheral portion of the silicon carbide single crystal ingot. Therefore, in the region upstream of the step flow growth surface inclined by the off angle (off upstream region), the number of TSDs necessary for maintaining the polymorphism is reduced, so that heteropolymorphism tends to occur and carbonization obtained The quality of the silicon single crystal substrate is degraded.

  This invention is made in view of this situation, and it aims at providing the silicon carbide single crystal ingot which reduced the number of TSD in the range which can maintain high quality. Moreover, it aims at providing the manufacturing method of the silicon carbide single crystal which makes it possible to sweep out the TSD which is inherent in the range which can maintain high quality.

  In order to solve the above-mentioned subject, the present invention adopts the following means.

(1) A silicon carbide single crystal ingot according to an aspect of the present invention is a silicon carbide single crystal ingot formed on a main surface having an offset angle with respect to a c-plane among surfaces of silicon carbide seed crystals, At a predetermined position in the crystal growth direction of the silicon carbide single crystal ingot, the central axis side of the silicon carbide single crystal ingot is at an outer peripheral portion excluding at least a part on the offset upstream side and including at least a part on the offset downstream side. With a necking section recessed into the

(2) In the silicon carbide single crystal ingot according to (1), the necking portion is preferably within a distance of 10 mm from the silicon carbide seed crystal.

(3) The silicon carbide single crystal ingot according to (1) or (2) has the necking portion, and the center of the cross section perpendicular to the crystal growth direction of the silicon carbide single crystal ingot is the above In plan view in the crystal growth direction, the distance from the center of the crystal growth surface of the silicon carbide seed crystal is preferably 2 mm or more.

(4) A method for producing a silicon carbide single crystal according to an aspect of the present invention is a method for producing a silicon carbide single crystal, wherein a silicon carbide raw material is disposed on one side in a crucible and the other in the crucible A silicon carbide seed crystal and a tubular guide member having an opening on one side facing the silicon carbide seed crystal are disposed on the side, and the center of the crystal growth surface of the silicon carbide seed crystal is in the crystal growth direction In plan view, the sublimation gas is supplied to the silicon carbide seed crystal in a state of being shifted from the center of the opening of the guide member.

(5) In the method for producing a silicon carbide single crystal according to (4), in plan view of the crystal growth direction, the center of the crystal growth surface of the silicon carbide seed crystal is from the center of the opening of the guide member. Preferably, the position of the silicon carbide seed crystal with respect to the guide member is adjusted so as to be separated in a range of 1 mm to 5 mm.

(6) In the method for producing a silicon carbide single crystal according to any one of (4) and (5), in the crystal growth direction, the crystal growth surface of the silicon carbide seed crystal is from the opening of the guide member It is preferable to adjust the position of the silicon carbide seed crystal with respect to the guide member so as to be separated in the range of 5 mm or less.

  The silicon carbide single crystal ingot of the present invention has a necking portion at an outer peripheral portion on the side other than the offset upstream side at a predetermined position in the crystal growth direction. The outer periphery of the offset upstream side does not have a necking portion. Therefore, while holding the TSD present on the upstream side of the offset, the TSD present on the outer peripheral portion other than the upstream side of the offset can be swept out by the necking unit. Therefore, the silicon carbide single crystal ingot according to the present invention suppresses the generation of heteropolymorphs on the upstream side, and reduces the number of TSDs present in the range in which high quality can be maintained.

  Further, in the method for producing a silicon carbide single crystal of the present invention, the TSD contained in the silicon carbide seed crystal propagates to the facet in the outer peripheral portion on the offset upstream side in the process of forming the silicon carbide single crystal ingot. In the outer peripheral portion on the side other than the side, it is swept out by the necking portion. Therefore, according to the method for producing a silicon carbide single crystal according to the present embodiment, silicon carbide single in which the number of inherent TSDs is reduced in a range in which generation of heteropolymorphism on the offset upstream side can be suppressed and high quality can be maintained. Crystals can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing (upper side) of the silicon carbide single crystal ingot which concerns on one Embodiment of this invention, and its seed crystal part, and a top view (lower side). It is sectional drawing of the manufacturing apparatus of the silicon carbide single crystal which concerns on one Embodiment of this invention. It is a figure which shows the manufacturing process of the silicon carbide single crystal which concerns on one Embodiment of this invention. It is the photograph to which some silicon carbide ingots obtained by the manufacturing method of the silicon carbide single crystal which concerns on one Embodiment of this invention were expanded.

  Hereinafter, the present invention will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, in order to make features of the present invention intelligible, the features that are the features may be shown enlarged for convenience, and the dimensional ratios and the like of each component are different from the actual ones. There is. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them, and can be appropriately modified and implemented within the scope of the effects of the present invention. .

(Silicon carbide single crystal ingot)
FIG. 1 is a cross-sectional view (upper side) along a crystal growth direction D of a silicon carbide single crystal ingot 101 according to an embodiment of the present invention and a seed crystal portion 102 serving as a base thereof. It is a top view (lower side). Silicon carbide single crystal ingot 101 is formed by step flow growth on the main surface of silicon carbide seed crystal 102 having an offset angle with respect to the c-plane.

  Silicon carbide single crystal ingot 101 is at a predetermined position P in the crystal growth direction D except at least a part on the upstream side in the offset direction when step-flow-growing a silicon carbide single crystal, and on the downstream side in the offset direction A necking portion (diameter reducing portion) 101c is provided in an outer peripheral portion (side wall surface 101a) including at least a part of

  Hereinafter, when the normal vector of the {0001} plane is projected onto the main surface of the base single crystal (seed crystal), the direction opposite to the direction of the projected vector is referred to as “offset direction”. In the silicon carbide single crystal ingot 101 of FIG. 1, the direction from the left to the right is the offset direction S. The side to which the projected vector is directed (right side) is referred to as "offset downstream side", and the opposite side (left side) is referred to as "offset upstream side".

Necking unit 101c, the silicon carbide single crystal ingot 101, a portion of the side wall surface 101a, which means the recess which has locally recessing the center axis C ₁ side. The center axis C ₁ of the silicon carbide single crystal ingot 101, passes through the center of the crystal growth surface 102a of the silicon carbide seed crystal, which means an axis extending in a direction perpendicular to the crystal growth surface 102a. In offset direction S, of the outer peripheral portion of the silicon carbide ingot 101, defined from the center axis C ₁ end S ₁ farthest portion on the downstream _side, the farthest portion on the upstream side and the end portion S _2.

As shown in the lower side of FIG. 1, the necking portion 101c is recessed inward from the position of the outer peripheral portion of the crystal growth surface 102a of the silicon carbide seed crystal 102 in plan view from the crystal growth direction D. The depth d ₁ of the recess is maximum at the end S ₁ of the offset downstream, it is preferable that smaller toward the offset upstream. The depth _{d 1} of the recess is at 1mm or more and preferably is 1mm or 5mm or less. If d ₁ is less than ₁ mm, dislocation sweeping may be insufficient, and if it is more than 5 mm, the diameter of the ingot is significantly reduced, so the amount of wafers obtained having a diameter equal to or greater than that of the seed crystal Will be reduced. The shape of the crystal growth surface 102 a is preferably circular, but may be polygonal.

  At least a part of the offset upstream side does not have a necking part, and this part protrudes outward from the position of the outer peripheral part of the crystal growth surface 102a in the plan view, or is recessed in the range of less than 1 mm inside It is.

Necking unit 101c, from the crystal growth surface 102a of the silicon carbide seed crystal, it is preferable that a distance _{d 2} within about 10 mm. In general, since dislocations decrease with distance from the seed crystal, it is preferable to provide a necking portion with diameter reduction close to the seed crystal in order to obtain a large-diameter, high-quality wafer.

  The cross-sectional view (upper side) of FIG. 1 illustrates the case where the necking portion 101c is recessed in a V shape with respect to the sidewall surface 102a of the silicon carbide single crystal ingot, but the shape of the necking portion 101c is There is no limitation. For example, the bottom surface of the recess forming the necking portion 101c may be flat or curved.

  The silicon carbide single crystal ingot formed by the conventional method is broadened as it is separated from the silicon carbide seed crystal so that the area of the cross section perpendicular to the crystal growth direction is larger than the area of the crystal growth surface of the silicon carbide seed crystal. It becomes a shape to diameter. On the other hand, in the silicon carbide single crystal ingot 101 of the present embodiment, as shown in the plan view (lower side) of FIG. 1, the diameter is locally reduced at the position P of the necking portion 101c. The area of the cross section 101b perpendicular to the above is smaller than the area of the crystal growth surface 102a of the silicon carbide seed crystal. The silicon carbide single crystal ingot 101 is expanded in diameter as it goes away from the necking portion 101 c in the crystal growth direction D.

  The center O 'of the cross section 101b of the silicon carbide single crystal ingot in the necking portion does not overlap with the center O of the crystal growth surface 102a of the silicon carbide seed crystal in plan view of the crystal growth direction D. The center O 'generally means the position of the center of gravity of the portion (small thickness portion) 101d near the cross section 101b, and the center O means the position of the center of gravity of the portion (minute thickness portion) 102b near the crystal growth surface 102a. ing. The position of the center O 'is preferably offset upstream by about 1 mm or more with respect to the position of the center O.

  At the offset upstream side, threading screw dislocations (TSD: indicated by broken lines) inherent in silicon carbide seed crystal 102 at the stage before crystal growth grow along with the silicon carbide single crystal, and the facet of silicon carbide single crystal ingot 101 Extends up to

  On the other hand, in the outer peripheral portion other than the offset upstream side, the TSD grown from the silicon carbide seed crystal 102 is swept out (removed) at the position P of the necking portion 101c, and a region with less TSD compared to the offset upstream side. Is formed.

  In silicon carbide members, there exist various polymorphs such as 3C, 4H, 6H, and 15R, which have different laminated structures. When a silicon carbide member is used as a wafer of the device, it is preferable to select a single polymorphic silicon carbide member. However, since there is almost no difference in Gibbs free energy among these polymorphs, multiple heteropolymorphs may be mixed into the silicon carbide member.

  One of the means for suppressing the heteropolymorphism contamination is to use a seed crystal in which the crystal face is turned off (tilted) 0 to 10 ° in the <11-20> direction from the C plane or the Si plane. In this method, since the step of determining the type of polymorph is exposed on the surface, the polymorph of the seed crystal is likely to be taken over.

  In the process of manufacturing silicon carbide single crystals, the {0001} plane (c plane) was turned off by 10 ° in the <11-20> direction in the growth of silicon carbide single crystals in order to suppress the occurrence of heteropolymorphism. Often used. Moreover, in order to suppress the generation of cracks (dislocations) and dislocations of the crystals constituting the ingot, it is preferable to reduce the temperature difference between the center and the outer periphery of the ingot. It is preferable that the difference in growth amount is a convex shape of 8 mm or less. However, when such a convex-shaped ingot is grown, facets of the C-plane or the Si-plane are formed off the upstream side. In the facet plane, heteromorphism tends to occur because step flow growth can not be performed.

  By conventional necking as disclosed in Patent Document 1, the ingot can be upgraded by mainly sweeping out dislocations in the outer peripheral portion of the ingot, but facets are easily formed off. The screw dislocation inherent upstream is also swept out. If there is a screw dislocation on the facet, a step is formed there, and the effect of making the polymorph stable is obtained. However, when conventional necking is performed, the screw dislocation is swept out. This effect is lost.

  In the silicon carbide single crystal ingot according to the present embodiment, by providing a region not necking only on the off-upstream side in the growth process, screw dislocations are easily present on the facets during growth, and heteropolymorphism is less likely to occur. Become. Then, since dislocations inherent in other portions are swept out by necking, the grown silicon carbide single crystal ingot has high quality. That is, according to the present embodiment, it is possible to achieve both the improvement in quality by dislocation sweeping and the suppression of heteropolymorphism contamination by maintenance of facet screw dislocation which were difficult in the prior art.

(Method of producing silicon carbide single crystal)
FIG. 2 is a longitudinal cross-sectional view of manufacturing apparatus 10 used for manufacturing a silicon carbide single crystal according to an embodiment of the present invention, and shows a state in which silicon carbide seed crystal 102 is disposed. The manufacturing apparatus 10 includes at least a crucible 11 and a raw material (silicon carbide raw material) 12 disposed on one side (lower side in FIG. 2) of the crucible 11 and the other side (upper side in FIG. 2) of the crucible 11 A pedestal (graphite member) 13 of a silicon carbide seed crystal (seed) 102, a tubular guide member 14 for guiding a source gas, and a coil 15 surrounding an outer wall of the crucible 11. The illustration of the depth portion of the coil 15 is omitted.

  The guide member 14 is disposed such that one opening 14 a faces the silicon carbide seed crystal 102 and the other opening 14 b faces the silicon carbide raw material 12. The inner diameter of one opening 14a of the guide member is about the same as the diameter of the crystal growth surface 102a of the silicon carbide seed crystal, specifically, at least 0.9 times and not more than 1.0 times the diameter of the crystal growth surface 102a. Is preferred.

From the viewpoint of guiding the source material distributed widely in the crucible 11 on the silicon carbide seed crystal 102, the guide member 14 has a side wall so as to reduce in diameter from the source 12 side to the pedestal 13 side. It is preferable to have a tapered shape. The guide angle (taper angle) between the central axis C ₂ of the side wall and the guide member 14 of the member 14 theta, is preferably 5 ° to 60 °. If the angle θ is smaller than 5 °, the diameter of the ingot is hardly expanded, which makes it difficult to obtain a large diameter wafer, which is not preferable. If the angle θ is larger than 60 °, expansion of the diameter of the ingot is promoted, but it becomes difficult to keep the temperature difference between the central portion and the outer peripheral portion of the growing ingot small and cracks and basal plane dislocations Is not preferable because it is likely to occur.

A manufacturing process of a silicon carbide single crystal using manufacturing apparatus 10 will be described. 3 (a) is, in a stage before performing the crystal growth, in the manufacturing apparatus 10 of a silicon carbide single crystal 2 is an enlarged view of a region R ₁ in the vicinity of the silicon carbide seed crystal 102. First, the silicon carbide seed crystal 102 is disposed in the crucible 11 in a state of being attached to the pedestal 13.

At this time, the crystal growth surface 102a, the position O "through which a central axis C ₂ of the guide member 14, than to be shifted to the offset position upstream of the center O, adjust the position of the silicon carbide seed crystal 102.

Furthermore, in plan view of the crystal growth direction D, the center O of the crystal growth surface 102a is separated from the center of the opening 14a of the guide member in the range of 1 mm to 5 mm, that is, position O and position O ′ ′ as the distance _{d 3} is 1mm or 5mm or less and it is preferable to adjust the position of the silicon carbide seed crystal 102 relative to the guide member 14.

Also, in the crystal growth direction D, the crystal growth surface 102 a contacts the opening (opening surface) 14 a of the guide member or separates from the opening 14 a of the guide member within 5 mm or less. It is preferable to adjust the position of the silicon carbide seed crystal 102. That is, it is preferable to adjust the position of silicon carbide seed crystal 102 with respect to guide member 14 so that distance d ₄ between crystal growth surface 102 a and opening 14 a is 5 mm or less.

3 (b) is in the stage of performing crystal growth, in the manufacturing apparatus 10 of a silicon carbide single crystal 2 is an enlarged view of a region R ₁ in the vicinity of the silicon carbide seed crystal 102. After arranging each component as described above, an alternating current is applied to the coil 15 to heat the crucible 11. As a result, a source gas (sublimation gas) is generated from the source 12, and the source gas is supplied to the silicon carbide seed crystal 102 installed on the pedestal 13 along the guide member 14. By supplying the raw material gas to the silicon carbide seed crystal 102, crystal growth of the silicon carbide single crystal ingot 101 is performed on the main surface of the silicon carbide seed crystal 102. The crystal growth surface 102 a of the silicon carbide seed crystal is preferably a carbon surface or a surface provided with an off angle of 10 ° or less from the carbon surface.

  Next, the obtained silicon carbide single crystal ingot 101 is sliced to prepare a silicon carbide single crystal wafer. The wafer is sliced in a direction perpendicular to <0001> or at an off-angle of 0 to 10 ° to prepare a wafer having a plane parallel to the c-plane or at an off-angle of 0 to 10 ° from the c-plane. The off angle may be provided in any direction. For example, when provided in the <11-20> direction, the angle between the main surface and the <11-20> direction is the offset angle. In the surface processing of the wafer, the (0001) plane side, ie, the Si surface side may be mirror-polished. The Si surface is a surface on which epitaxial growth is usually performed.

  As described above, the TSD contained in the silicon carbide seed crystal 102 propagates to the facet in the outer peripheral portion on the offset upstream side in the process of forming the silicon carbide single crystal ingot 101, but the outer peripheral portion on the side other than the offset upstream side Then, it is swept out by the necking unit 101c. Therefore, according to the method for producing a silicon carbide single crystal according to the present embodiment, silicon carbide single in which the number of inherent TSDs is reduced in a range in which generation of heteropolymorphism on the offset upstream side can be suppressed and high quality can be maintained. Crystals can be produced.

  In the present embodiment, an example in which the sublimation method is applied is described as a method for producing a silicon carbide single crystal, but an apparatus having a configuration corresponding to the above-mentioned guide member on a silicon carbide seed crystal is used to It is also possible to apply a gas method to grow from the above.

  Hereinafter, the effects of the present invention will be made more apparent by examples. The present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist of the invention.

Example 1
The manufacturing method of the silicon carbide single crystal concerning the said embodiment was implemented. FIG. 4 is an enlarged photograph of the necking portion on the offset downstream side in the silicon carbide single crystal ingot obtained in the manufacturing process. Enlarged portion corresponds to a portion of the region R ₂ shown in FIG. 3, as in the above embodiment, with respect to the central axis of the guide member, the center of the silicon carbide seed crystal is shifted in the offset downstream.

As a silicon carbide seed crystal, a crystal growth surface having a diameter of about 160 mm and a thickness of about 2 mm was used. As a guide member, one having an inner diameter of about 158 mm in the opening at the silicon carbide seed crystal side and a taper angle of about 15 ° in the side wall was used. When placing the pedestal of the silicon carbide seed crystal, in a plan view of the crystal growth direction, and the center of the crystal growth surface of the silicon carbide seed crystal, the distance d ₃ between the center of the opening of the guide member, was about 1mm . Furthermore, the crystal growth surface of the silicon carbide seed crystal, the distance d ₄ between the opening portion of the guide member, was about 0.5 mm.

As described above, by performing the sublimation method after adjusting the position of the silicon carbide seed crystal with respect to the guide member, it has been confirmed that the necking portion is formed as shown in FIG. In the necking portion, the depth of the depression on the central axis side (left side) was maximum at a position d ₂ of about 4 mm from the crystal growth surface. The depth d ₁ of the recess about 2mm, and the in a plan view of the crystal growth direction, the center position of the crystal growth surface, was at a distance approximately equal offset from the center position of the opening of the guide member.

  Observation by X-ray topography revealed that the TSD propagation from the silicon carbide seed crystal side (upper side) ceased at the position of the necking portion and was not present in the portion grown after the necking portion . From this result, it was possible to confirm that the TSD was swept out in the necking section.

  The present invention can be utilized when growing a SiC single crystal by a sublimation method or the like, reduces the generation of threading screw dislocations that affect the characteristics of a device using a SiC single crystal, and contributes significantly to the improvement of yield. Provide a means to

101 ··· Silicon carbide single crystal ingot 101a · · · Side wall surface 101b · · · Cross section 101c · · · Necking section 101d · · · · · · · · 102 silicon carbide seed crystal 102a · · · · crystal growth surface 102b ... Part 10 in the vicinity of the crystal growth surface ... ... Manufacturing device ... ... ... ... ... ... ... ... ... ... ... ... Raw material ... 13 ... ... Guide members 14a, 14b ... Openings ... ... Coils C ₁ , C ₂ ... central axis D ... crystal growth direction d ₁ , d ₂ , d ₃ , d ₄ ... distance O, O ', O ", P ... position R ₁ , R ₂ · · · · Region S · · · offset direction S ₁ , S ₂ · · · · end portion θ ... angle

Claims (6)

A silicon carbide single crystal ingot formed on a main surface having an offset angle with respect to a c plane among surfaces of a silicon carbide seed crystal,
At a predetermined position in the crystal growth direction of the silicon carbide single crystal ingot, the central axis side of the silicon carbide single crystal ingot is at an outer peripheral portion excluding at least a part on the offset upstream side and including at least a part on the offset downstream side. What is claimed is: 1. A silicon carbide single crystal ingot characterized by having a necking portion recessed in the above.   The silicon carbide single crystal ingot according to claim 1, wherein the necking portion is at a distance of 10 mm or less from the silicon carbide seed crystal.   The center of the cross section perpendicular to the crystal growth direction of the silicon carbide single crystal ingot having the necking portion is separated by 1 mm or more from the center of the crystal growth surface of the silicon carbide seed crystal in plan view of the crystal growth direction The silicon carbide single crystal ingot according to any one of claims 1 or 2, characterized in that: A method for producing a silicon carbide single crystal, comprising
Place the silicon carbide source on one side of the crucible,
On the other side in the crucible, a silicon carbide seed crystal and a tubular guide member having an opening on one side facing the silicon carbide seed crystal are disposed;
Supplying a sublimation gas to the silicon carbide seed crystal in a state where the center of the crystal growth surface of the silicon carbide seed crystal is shifted from the center of the opening of the guide member in plan view of the crystal growth direction; Method of producing silicon carbide single crystal.   The carbonization of the guide member is performed such that the center of the crystal growth surface of the silicon carbide seed crystal is separated from the center of the opening of the guide member in the range of 1 mm to 5 mm in plan view of the crystal growth direction. The method for producing a silicon carbide single crystal according to claim 4, wherein the position of the silicon seed crystal is adjusted.   Adjusting the position of the silicon carbide seed crystal with respect to the guide member such that the crystal growth surface of the silicon carbide seed crystal is separated in the range of 5 mm or less from the opening of the guide member in the crystal growth direction; The method for producing a silicon carbide single crystal according to any one of claims 4 or 5, characterized in that